1. Field of the Invention
The broad object of the invention is an invention for protecting electronic circuits, such as integrated circuits, against electrostatic charges, and it applies particularly to the protection of integrated circuits mounted on an electrically insulating carrier element, with the assembly (integrated circuits/carrier element) forming, for instance, a portable data carrier of the "credit card" type.
2. Description of the Prior Art
The advent of microprocessors has made possible popularization of data processing techniques in mass market applications of credit cards. Such personalized portable data carriers or "credit cards" are currently under development. A typical banking data processing application is described in the September 1980 issue of the American Banking Association (ABA) Journal in the article by Mr. Bill Orr, "The chip card is here, but where is it going?" A typical medical data processing application is described in the promotional flyer of the assignee of the present invention, Cii Honeywell Bull, emitted "Individual Cardiology file on CP8 memory card" which appeared as a supplement in "The Communicator", a marketing communication service publication of Cii/HB, dated June, 1981. Such a card consists of a carrier element with electrically insulated integrated circuits, which allow data input of a general and confidential nature, and it also permits internal and external processing of this data.
Generally speaking, an integrated circuit consists of a chip with a few s1uare millimeters of surface, on one face of which are mounted electronic circuits, including fixedinput/output contacts connected by leads to an interconnecting net mounted on the carrier element. This interconnecting net includes input/output terminals which can be reached from the outside to allow the necessary outside connections to be made.
To improve the mechanical, thermal and electrical properties of such a card, there is usually provided a protective device for the IC's (integrated circuits) consisting of an electrically insulating coating, which partially covers the card-carrying element, while leaving the input/output terminals accessible.
In view of its nature and portable character, such a card is, of course, likely to be subject to the action of electrostatic charges produced particularly by the effect of various frictions to which the card-carrying element could be subjected while not in use.
The action of these electrostatic charges is all the more sensitive because these IC's usually require high-insulation technologies such as, for instance, the MOS technology, which offers the advantage of high-density integration. Indeed, the MOS technology, and particularly the N. MOS technology, affords certain protections against all kinds of electrostatic charges, which could destroy the circuits by short-circuiting the GATE-SOURCE gaps.
The invention aims at overcoming this inconvenience by using a protective device designed to insulate mainly the above mentioned input/output terminals, which are accessible from the outside, to prevent the electrostatic charges, which are loaded at the level of the card-carrying element and which are distributed over this carrier element as a function of the various frictions to which it could be exposed, from creating microarcs which are likely to spark by point effect between the carrier element and one of the input/output terminals of the card.